OP0115 DISTURBED SPATIAL WNT ACTIVATION - A POTENTIAL MEDIATOR OF DISTURBED SKIN POLARIZATION IN SYSTEMIC SCLEROSIS (SSC)
Authors: S. Chenguiti Fakhouri, L. Konstantinidis, Z. Honglin, M. Eckstein, C. Dees, A. Kreuter, M. Sticherling, G. Schett, D. Jörg, C. Bergmann
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Disruption of the skin structure is a central hallmark of Systemic Sclerosis (SSc). Healthy adult human dermis is characterized by a papillary dermis (conic upward papillae with nerve endings, mechanoreceptors, vessels and loose collagen bundles) and a reticular dermis (coarse collagen bundles). In SSc, the dermal structure is disrupted and shifted towards a "reticularized" phenotype with loss of dermal papillae and exaggerated deposition of collagen. Little is known on mechanisms necessary to maintain physiological adult human skin morphology. Evidence from murine experiments suggests that short distance morphogen gradients are necessary for three-dimensional pattern formation in embryonic skin morphogenesis in rodents [1]. <h3>Objectives:</h3> 1) to analyze if spatial WNT/β-catenin activation is observed in adult healthy human skin and whether it is altered in fibrosing skin disorders such as SSc 2) to assess whether perturbation of spatial WNT/ β-catenin activation correlates with disruption of physiological skin structure in SSc 3) to analyze whether spatial activation is mimicked in a Wnt-driven murine fibrosis model and can be reverted by overexpression of the endogenous Wnt-antagonist Dkk1 <h3>Methods</h3> Dermal skin morphology was quantitatively assessed using HE and trichrome staining of skin sections of 40 SSc patients and 18 healthy controls. Enrichment of papillary and reticular marker genes and WNT target genes in healthy and SSc skin transcriptome were assessed by gene set enrichment analyses using prepublished datasets [2]. Spatial WNT/β-catenin activation was analyzed by RNAscope-in situ hybridization detection of <i>AXIN2</i>. Immunofluorescence (IF) staining was performed to detect β-catenin distribution. In addition, skin sections of Wnt10btg- and Dkk/Wnt10btg mice were analyzed. <h3>Results</h3> Here we quantitatively describe a marked decrease of number, area and height of papillary structures in SSc compared to healthy controls. Consistently, papillary/reticular marker gene expression is shifted towards a reticular profile in SSc skin compared to controls. Next, we analyzed whether the expression of WNT3A-regulated target genes is enriched in papillary or reticular gene sets of healthy skin. We observed an enrichment of WNT3A-regulated target genes in papillary gene sets of healthy skin. Consistently, we observed a distinct pattern of spatial distribution of β-catenin-expressing fibroblasts in healthy skin that is disturbed in SSc: In healthy skin, β-catenin-positive fibroblasts were predominantly located in the papillary dermis and the relative amount of β-catenin-expressing fibroblasts was reduced in the reticular part. In contrast, in SSc skin, we observed a 2-fold increase of β-catenin-positive fibroblasts throughout the dermis. A gradient with enrichment of β-catenin-expressing fibroblasts in the papillary layer as observed in healthy skin was no longer detectable in SSc. Confocal imaging suggested increased nuclear accumulation of β-catenin in the reticular dermis compared to the papillary dermis in SSc skin. The loss of spatial WNT activation in SSc was confirmed on a transcriptional level. Interestingly, spatial redistribution of WNT activation is mimicked in Wnt10btg mice compared to wild-type mice and partially reverted by overexpression of the endogenous Wnt antagonist Dkk1. These results suggest that distinct site-specific activation of WNT/β-catenin signaling with a delicate balance of WNT agonists and antagonists might be necessary to maintain and eventually restore physiologic skin integrity in adult human skin. <h3>Conclusion</h3> Our study presents first evidence for a loss of the physiological β-catenin gradient in SSc, associated with a loss of papillary dermal structure. Further analyses of WNT agonists and antagonists spatial distribution and advanced in vitro models mimicking a papillary skin structure will be necessary to better understand mechanisms of skin structure maintenance in healthy adult human skin. <h3>References</h3> [1]Matos et al. Elife 2020 [2]Skaug, Khanna et al. Ann Rheum Dis. 2020 <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> Sara Chenguiti Fakhouri: None declared, Laura Konstantinidis: None declared, ZHU Honglin: None declared, Markus Eckstein: None declared, Clara Dees: None declared, Alexander Kreuter: None declared, Michael Sticherling: None declared, Georg Schett: None declared, Distler Jörg Shareholder of: JHWD is stock owner of 4D Science and scientific lead of FibroCure., Consultant of: JHWD has consultancy relationships with Actelion, Active Biotech, Anamar, ARXX, Bayer Pharma, Boehringer Ingelheim, Celgene, Galapagos, GSK, Inventiva, Medac, Novartis, Pfizer, RuiYi and UCB., Grant/research support from: JHWD has received research funding from Anamar, Active Biotech, Array Biopharma, ARXX, aTyr, AstraZeneca, BMS, Bayer Pharma, Boehringer Ingelheim, Cantargia, Celgene, CSL Behring, Galapagos, GSK, Inventiva, Kiniksa, Sanofi-Aventis, RedX, UCB., Christina Bergmann Consultant of: CB has received consultancy fees from Pfizer and Boehringer-Ingelheim.